During the first three weeks of May, the planets Venus, Mercury, Mars, and Jupiter will cluster in our predawn sky for some spectacular groupings. In August 2010, a similar gathering of planets graced our evening sky. Seen in
this image are the crescent moon and the bright planet Venus, with Mars to Venus' upper left and Saturn to its right.

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NASA has declared 2011 the Year of the Solar System because of an unprecedented number of space missions to planets, moons, comets and asteroids that will culminate or begin this year. The coming year is full of cool cosmic events, natural and NASA-made, and a day-by-day listing is included here. I’ve condensed the long list down to my top 10 celestial events for 2011:

Jan. 8 and 9

Double morning stars: The solar system’s two innermost planets, Mercury and Venus, behave differently than the rest of the planets. Instead of being free to wander around the sky, they are tethered to the sun so that they seem to swing out from one side of the sun to the other and back. Each planet spends a brief time as our evening star followed by a brief engagement as our morning star. The best time to catch each planet is when it is near its greatest angular distance from the sun, an event called greatest elongation. Even at greatest elongation, Mercury is never more than 28 degrees and Venus never more than 48 degrees from the sun. Early this month, both planets will reach their greatest elongations west of the sun within one day of each other, providing an unusual opportunity to see Mercury and Venus at their best. Before dawn Jan. 8, Venus will stretch 47 degrees west of the sun and rise more than three and a half hours before the sun does. On Jan. 9, Mercury reaches its greatest elongation 23 degrees west of the sun, rising about one and a half hours before the sun. On either morning, if you face the southeast at about 6:15 a.m. and have a clear view to the horizon, you can spot both planets glimmering in the dawn sky.

Feb. 14

To the heart of a comet: This Valentine’s Day, NASA plans to shoot an arrow through the heart of a comet, figuratively speaking. The target: Comet Tempel 1. The arrow: the Stardust spacecraft. Comet Tempel 1 already was the target of the Deep Impact spacecraft in 2005, which blasted a hole in the side of the comet with an 800-pound copper bullet and splattered comet dust across the inner solar system. The Stardust spacecraft was the first to return a sample of a comet to Earth in 2006 after swooping through the dusty tail of Comet Wild 2. Now, in an historic example of cosmic recycling, the Stardust spacecraft has been re-targeted for Comet Tempel 1. The follow-up mission hopes to accomplish several scientific goals, including a clear view of the crater blasted by Deep Impact. Using the same spacecraft instrumentation to explore two comets will tell us about the differences and similarities between comet nuclei. Visit the Stardust Mission website for more details at http://stardustnext.jpl.nasa.gov/.

March 18

A MESSENGER for Mercury: Someone at NASA had to really stretch their imagination to come up with an acronym for the Mercury-bound spacecraft, MESSENGER. The letters stand for MErcury Surface, Space ENvironment GEochemistry and Ranging. Launched from Earth on Aug. 3, 2004, MESSENGER has been swinging around Earth and Venus in an epic game of celestial billiards for the past six years in order to get MESSENGER to its target: Mercury. MESSENGER actually has zoomed past Mercury three times in the years since its launch, but during its next pass March 18, MESSENGER will fire its braking engine and become the first space probe to orbit Mercury. From orbit, MESSENGER will be able to map Mercury’s surface, determine the composition of its surface rocks and minerals, and study the nature and source of its magnetic field. Mercury has been mostly unexplored; the only previous spacecraft to zoom past it, Mariner 10, was back in the mid-1970s. For more information, check out NASA’s MESSENGER website at http://messenger.jhuapl.edu/.

April 3

The rings of spring: Once every 378 days, the Earth gains a lap on the sluggish planet Saturn and passes between Saturn and the sun, placing the two planets as close together as possible. This alignment of worlds is called opposition. When Saturn reaches opposition April 3, it will be 804 million miles from Earth, its closest point for 2011. Saturn will rise in the eastern sky at sunset and shine in our sky all night among the stars of the constellation of Virgo, not far from the equally bright stars Arcturus and Spica. Any telescope aimed at Saturn will reveal the beautiful system of rings encircling its equator and the largest of its many moons: Titan. After turning themselves edgewise to Earth in 2009 and briefly disappearing from view, the rings are opening up to us again in all of their splendor. Point that telescope at Saturn in April. You won’t believe your eyes.

April 30

A parade of planets: During the last week of April and the first two weeks of May, our predawn sky will be buzzing with activity as the planets Mercury, Venus, Mars and Jupiter cluster and glide past one another. To see that many bright planets in such a tight grouping is a remarkable sight and one that you will not soon forget. The fun begins at about 5 a.m. April 30 when the thin crescent moon and Venus first rise above the eastern horizon. Mercury follows moments later and the Mars-Jupiter pair appears after that. The moon, Venus and Jupiter should be easy to spot, but Mercury and Mars will be a little more challenging in the brightening sky. During the following three weeks, watch for Mars to pass 0.4 degrees from Jupiter on May 1, Mercury to pass 1.5 degrees from Venus on May 7, Jupiter and Venus to pass within 0.5 degrees of each other May 11, Mercury to pass 2 degrees from Mars on May 21 and Mars to pass 1 degree from Venus on May 23. Saturn is the only planet visible by the naked eye that is not participating in this planet parade.

Aug. 14

Dawn at Vesta: NASA’s Dawn spacecraft has been maneuvering toward the mysterious asteroid Vesta since its launch Sept. 27, 2007. Vesta is the second-largest of the thousands of asteroids that circle the sun in the asteroid belt between the orbits of Mars and Jupiter. Hubble Space Telescope images of this Colorado-sized asteroid reveal hints of bright craters and dark lava flows and what appears to be a colossal impact crater at Vesta’s south pole. The central mountain peak in this gaping 300-mile-diameter hole rises 11 miles, twice the height of Earth’s Mount Everest. About 200 space rocks called HED meteorites that have fallen to Earth are thought to be fragments thrown from this violent impact. The Dawn spacecraft is scheduled to arrive at Vesta and settle in to orbit it Aug. 14. After scrutinizing Vesta’s surface and environment for 11 months, Dawn again will fire up its ion engine and depart for its second target, the largest of the asteroids and dwarf planet designate, Ceres. Dawn will arrive at Ceres in February 2015 and will orbit and study this water-rich world for several months. By exploring these two enigmatic mini-worlds in the asteroid belt, we hope to learn more about the history of our own world and the dawn of our solar system. For more information, visit NASA’s Dawn mission website http://dawn.jpl.nasa.gov.

Oct. 1

Mars in the beehive: The heavenly highway used by the sun, moon and planets as they whirl around the sky passes through the 12 constellations of the zodiac. Along this path, there are four glittering star clusters through which the planets can pass: Pleiades, Hyades, M35 and Beehive. I am partial to these close encounters between planets and star clusters because the sight of a bright planet surrounded by dozens of twinkly little stars just makes me smile. So I am looking forward to Oct. 1 when Mars will pass through the Beehive star cluster in Cancer the Crab. Any time between 3 a.m. and dawn, you will find Mars and the Beehive high in the eastern sky. Although Mars is very bright and the Beehive is faintly visible to the unaided eye, binoculars or a small telescope will be required for the best view of this event. The telescopic view should resemble a bag full of sparkling diamonds with one big, radiant ruby in the mix.

Oct. 7 and 8

Catch a falling star: 2011 is a dismal year for meteor watching, as the full or nearly full moon spoils all of our favorite annual meteor showers: August’s Perseids, November’s Leonids and December’s Geminids. The one bright spot for meteor watchers this year comes from what usually is a minor meteor shower called Draconids. If forecasters are right, we could be in for a spectacular rain of meteors Oct. 7 and 8. Estimates for this year’s shower are as many as 750 meteors per hour streaking across the sky. That’s the good news. The bad news is that the peak is expected to occur over Europe, not North America. Still, the prospects for seeing dozens of meteors per hour over the U.S. should be enough to get any meteor enthusiast outdoors and looking up. The Draconid meteors will seem to rain down from the head of Draco the Dragon, not far from the bright star Vega, high in our northwestern sky after sunset. The nearly full moon will interfere somewhat, but just put the moon to your back and watch the sky anyway.

Oct. 28

The Halloween king: Venus has the distinction of being the brightest planet visible in the sky, but Venus always is seen near the horizon at dusk or dawn, never high overhead in our midnight sky. Jupiter wears the crown when it comes to ruling the midnight sky, and Jupiter will be at its closest point to Earth in 2011 on Oct. 28 when it reaches opposition. For several weeks around that date, Jupiter will rise in the east as the sun goes down in the west and gleam brilliantly high in our midnight sky. On the night of opposition, Jupiter will be a mere stone’s throw from Earth, about 371 million miles. Steady binoculars or any small telescope will reveal Jupiter’s four traveling companions, discovered by Galileo in 1610. They are Io, Europa, Ganymede and Callisto, the four largest of Jupiter’s 63 known moons. Watch from night to night as the moons shift their positions around Jupiter. With a medium-size telescope, you can also see the two main cloud stripes straddling Jupiter’s equator and maybe even the famous red spot. In fall, Jupiter will shine down on us from the constellation of Aries the Ram. Look for a distinctive little triangle of bright stars just above Jupiter. That’s Aries. When you are out trick-or-treating on Halloween, glance up at that dazzling planet lighting your way after dark. It’s Jupiter, the king of the Halloween sky.

Dec. 10

A brush with totality: This will be a six-eclipse year, with four partial solar eclipses and two total lunar eclipses. North America, though, is on the wrong side of the Earth for all of these eclipses except one. On Dec. 10., the western U.S. will get to see the first half of a total eclipse of the moon. Unlike the spectacular total lunar eclipse Dec. 21, 2010, the moon will set for Coloradans just as the total phase of the eclipse begins. Early risers can watch the eclipse begin in a dark sky at 5:46 a.m. when the top edge of the moon will begin to darken as it slips into the Earth’s shadow. Then, as the eclipse progressively gobbles up more of the full moon, the sky will begin to brighten with the morning dawn. Eventually, the sky will become so bright that the eclipsed moon likely will fade from view as it sinks toward the western horizon. Totality begins at 7:06 a.m., the sun rises at 7:18 a.m., and the moon sets at 7:21 a.m. Lousy timing for folks living in Northwest Colorado, but perfect for folks living in Alaska and Hawaii, who will get to see the entire eclipse. This is the closest that we will come to a total lunar eclipse until April 15, 2014, so you’d better enjoy this brush with totality.

Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His Celestial News column appears weekly in the Steamboat Today, and his Cosmic Moment radio spots can be heard on local radio station KFMU. For a full-color wall calendar of celestial events in 2011 featuring some of Jimmy’s best astrophotos, visit www.jwestlake.com.